Re: [PATCH v2] mac80211: LLVMLinux: Remove VLAIS usage from mac80211

On 03/07/14 18:27, Joe Perches wrote:

On Fri, 2014-03-07 at 18:15 -0800, Behan Webster wrote:

quoted

On 03/07/14 17:56, Joe Perches wrote:

quoted

On Fri, 2014-03-07 at 17:26 -0800, behanw@converseincode.com wrote:

quoted

From: Jan-Simon Möller <redacted>

Replaced the use of a Variable Length Array In Struct (VLAIS) with a C99
compliant equivalent. This is the original VLAIS struct.

[]

quoted

diff --git a/net/mac80211/aes_ccm.c b/net/mac80211/aes_ccm.c

[]

quoted

@@ -23,12 +23,14 @@ void ieee80211_aes_ccm_encrypt(struct crypto_aead *tfm, u8 *b_0, u8 *aad,
   			       u8 *data, size_t data_len, u8 *mic)
   {
   	struct scatterlist assoc, pt, ct[2];
-	struct {
-		struct aead_request	req;
-		u8			priv[crypto_aead_reqsize(tfm)];
-	} aead_req;
   
-	memset(&aead_req, 0, sizeof(aead_req));
+	char aead_req_data[sizeof(struct aead_request) +
+				crypto_aead_reqsize(tfm) +
+				CRYPTO_MINALIGN] CRYPTO_MINALIGN_ATTR;

Can this be a too large amount of stack?

Is crypto_aead_reqsize() limited to < ~1k?

Perhaps it'd be better to use kzalloc for this
or another reserved pool

No more stack being used than with the the original code. The stack
memory use is identical.

I do understand that, but that's not my question.

I appreciate you're getting this to compile for llvm.

Any idea of the max value of crypto_aead_reqsize?

And I understand your question, as well as why it is important.

Moving it from being stack based to alloacted memory may or may not be a good thing, but is orthogonal to the intention of this particular patch (which is just to remove the use of VLAIS from this code).

$ grep-2.5.4 -rP --include=*.[ch] "(?:->|\.)\s*\breqsize\s*=[^=][^;]+;" *

Very clever. I'm going to use this. :)

Behan

-- 
Behan Webster
behanw@converseincode.com